The present disclosure relates to an image forming apparatus provided with a transferring device which transfers a toner image formed on an image carrier to a sheet.
In an image forming apparatus, such as a copying machine, a printer or a multifunction peripheral, a toner image formed on an image carrier is transferred to a sheet by a transferring device. In the transferring device, the sheet is guided along a guide to a transferring nip formed between the image carrier and a transferring member, and a transferring bias is applied to the transferring member to transfer the toner image to the sheet.
In order to prevent toner scattering due to pre-transfer or an image failure due to abnormal electric power discharge, the sheet is guided by the guide so as to come into contact with the image carrier as close as possible before the transferring bias is applied. However, if a sheet with a large thickness, such as a postcard, is guided by a fixed guide set suitably for a sheet of plain paper, since a load applied to the sheet from the guide is increased due to the thickness or hardness of the sheet, a sheet conveying speed may become slow and thereby a magnification changes or an image failure such as a dot blank may occur.
In order to prevent occurring of such an image failure caused by the fixed guide, there is an image forming apparatus having a rigid guide which is turnably provided such that one end is elastically biased in the direction of the image carrier. Also, there is an image forming apparatus having a guide supported such that one end on the side of the image carrier is deflected. In addition, there is an image forming apparatus having a flexible guide and a buffering member which is formed on the lower face of the flexible guide so as to protrude in a direction of the image carrier over the flexible guide. Further, there is an image forming apparatus having a flexible guide which is swingable in the direction of the image carrier, in which the guide is prevented from swinging toward an opposite side to the image carrier by a protrusion part.
However, in the case of the turnable rigid guide of which one end is elastically biased in the direction of the image carrier, it is difficult to adjust a biasing force with respect to a sheet which is different in thickness, width and rigidity. For example, if the rigid guide is set with respect to the image carrier as close as possible so as to be suitable for a sheet of plane paper, a conveying load applied on a sheet of postcard increases and thus an image failure, such as a dot blank, on the postcard cannot be restricted. In order to restrict such an image failure, it is necessary to attach an expensive low friction member, resulting in higher costs. Also, in a case of the guide of which one end on the side of the image carrier is deflected, a horizontal strip, character blurring or the like easily occur due to vibration generated when the rear end of the sheet is spaced away from the guide. In addition, in a case of the guide provided with the buffering member, since a friction between the buffering member and the sheet occurs, the back face of the sheet may be soiled or abrasion of the buffering member may occur. Further, in a case where the guide is prevented from swinging on the opposite side to the image carrier, since a height at which the rear end of the sheet is spaced from the guide varies depending on rigidity of the sheet, an image failure easily occurs at the rear end of the sheet.